Java Usage of JScrollPane

I need to draw inside a JScrollPane, which I thought meant dropping a JPanel or a Canvas or something into a JScrollPane which itself had been dropped into a JFrame. It Ain't Necessarily So!

What I have below is an annotated listing of my first success. Part of the code is stolen from SUN's jswing documentation and tutorials. In general, what is shown in blue is stuff generated by the IDE (not completely, however), and what is shown in black is my typing (I hope you know what I mean). I will annotate the text in color comments which should be self evident as to whether they are code or comments.

 

/*
 * ScrollTest2.java
 *
 * Created on August 7, 2003, 10:04 AM
 */

/**
 *
 * @author  C. W. David
 * as helped by Tim Boudreau at SUN
 */

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;

//added to get addWindowListener(this) to work
// after adding jScrollPane1


public class ScrollTest2 extends javax.swing.JFrame implements WindowListener{


//"implements WindowListener" added after dropping JScrollPane into JFrame


    
    /** Creates new form ScrollTest2 */
    public ScrollTest2() {
        initComponents();

        MyComponent figure = new MyComponent();
        jScrollPane1.add(figure);
        //the following are all required to get scrolling to take place:
        figure.setPreferredSize(new Dimension(600,600));

//the above is set large enought to exceed the frame size(below)

        jScrollPane1.setViewportView(figure);
        //end of scrolling required matters.
        int frameWidth = 400;
        int frameHeight = 400;
        this.setSize(frameWidth, frameHeight);
        this.setVisible(true);
    }
    
    /** This method is called from within the constructor to
     * initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is
     * always regenerated by the Form Editor.
     */
    private void initComponents() {//GEN-BEGIN:initComponents
        jScrollPane1 = new javax.swing.JScrollPane();

        addWindowListener(this);

        getContentPane().add(jScrollPane1, java.awt.BorderLayout.CENTER);

        pack();
    }

    // Code for dispatching events from components to event handlers.

    public void windowActivated(java.awt.event.WindowEvent evt) {
    }

    public void windowClosed(java.awt.event.WindowEvent evt) {
    }

    public void windowClosing(java.awt.event.WindowEvent evt) {
        if (evt.getSource() == ScrollTest2.this) {
            ScrollTest2.this.exitForm(evt);
        }
    }

    public void windowDeactivated(java.awt.event.WindowEvent evt) {
    }

    public void windowDeiconified(java.awt.event.WindowEvent evt) {
    }

    public void windowIconified(java.awt.event.WindowEvent evt) {
    }

    public void windowOpened(java.awt.event.WindowEvent evt) {
    }//GEN-END:initComponents
    
    /** Exit the Application */
    private void exitForm(java.awt.event.WindowEvent evt) {//GEN-FIRST:event_exitForm
        System.exit(0);
    }//GEN-LAST:event_exitForm
    
    /**
     * @param args the command line arguments
     */
    public static void main(String args[]) {
        new ScrollTest2().show();
    }
    
    
    // Variables declaration - do not modify//GEN-BEGIN:variables
    private javax.swing.JScrollPane jScrollPane1;
    // End of variables declaration//GEN-END:variables


//Here is where the learning (from Tim Boudreau at SUN) comes.
//One needs to have the paint routine inside some kind of container
//so that the container can be scrolled, and the painting only extends to
//the boundaries of the container.
//This, and the next example, show ways to do this.
//This example is the simplest.

    class MyComponent extends JComponent{
        public void paint(Graphics g){
            Graphics2D g2d = (Graphics2D)g;
            int x=0;
            int y=0;
            int width = getSize().width - 1;
            int height = getSize().height - 1;
            g2d.drawLine(0,0, width,height);
            g2d.drawOval(x,y, width,height);
        }
    }
}

Return to the main book TOC.